Cement compositions are generally prepared at the point of use by combining cement mortars, i.e. dry mixtures comprising not less than 10 weight percent cement, based on the total dry weight of the mortar, with an amount of water sufficient to enable the application of the resultant cement composition to a surface prior to it setting and hardening upon drying. Such cement compositions can be used as adhesive compositions, in particular tile adhesive compositions, strongly holding two surfaces together once the setting process has completed.
Conventional cement compositions often comprise a combination of cement and one or more additives, such as sand, lime, dispersants, thickeners and plasticizers, which provide a modified cement composition with improved physical characteristics. In particular, the use of fine aggregate materials such as silica sand is well known. Further, wetting agents or water retention additives may be utilized to impart a beneficial effect upon the physical characteristics of the cement composition and/or the resultant hardened product, which are highly dependent upon both the initial hydration process and the subsequent water removal as the composition sets and hardens upon drying. For example, the incorporation of wetting agents or water retention additives may lead to increase in open time, setting rate and drying time.
The use of polysaccharide derivatives, in particular, water soluble cellulose ether compounds, as water retention additives in cement compositions is well known. For example, U.S. Pat. No. 4,402,752 discloses a dry-set mortar composition adapted to be mixed with water containing, in the dry state, sand, Portland cement and cellulose ether improved by the inclusion of anionic polyacrylamide and bentonite clay. There is no disclosure in this document of the use of a redispersible polymer powder in the compositions.
In addition to cellulose ether, cement compositions are known to contain other additives. For example US-A-2005/0241539 discloses a mixture composition for use in preparing tile cement compositions, wherein the resultant dry tile cement comprises from 0.1 to 2.0 weight percent alkylhydroxyalkyl cellulose and/or hydroxyalkyl cellulose prepared from raw cotton linters and 0.0001 to 15 weight percent of at least one additive. Included amongst a long list of specific additives generically disclosed in this document are redispersible polymer powders, gelatin and bentonite. However, this document fails to provide any disclosure of a single composition comprising a cellulose ether, a redispersible polymer powder and an additive selected from gelatin, bentonite and combinations thereof.
Redispersible polymer powders (RDP) made from emulsion polymers, such as vinyl acetate/ethylene copolymers, styrene/butadiene copolymers, and vinyl acetate/versatic acid vinyl ester copolymers are widely used in various construction applications, such as cement-containing tile adhesives (CBTA) to improve the mechanical properties such as tensile adhesive strength of the cementitious composition.
Whilst conventional cement dry mortars may typically contain a variety of additives in order to improve the physical characteristics of the resultant cement composition, either in the wet or dry hardened state, there remains a desire to obtain a reduction in setting time within RDP and cellulose ether containing cement compositions without causing any significant detrimental effects on the performance or properties of such compositions. In addition, there remains a desire to obtain an increase in slip resistance within RDP and cellulose ether containing cement compositions without causing any significant detrimental effects on the performance or properties of such compositions. In particular, it would be advantageous to obtain both a reduction in setting time and an increase in slip resistance without causing any significant detrimental effects on the performance of such compositions.